Hi
the below is list of what I understand can be claimed

The interest on the mortgage
Rental insurance
Any maintenance of the property
Letting agency fees
10% of the rental income each year to cover depreciation in the value of furnishings, including sofas and carpets (this does not include fittings such as kitchen units and bathroom suites)

as my gf is trying to juggle mortgage/ early repayment penalties, retiring etc is there ‘calcultor’ type site that will lets us plug the numbers in to see how changes will impact her income

thanks

sounds about right going by my self-assessment, letting agency also charged tax on my fee’s, so that added to the offset too (not huge but it all adds up).

threw it all into a spreadsheet for ours, no receipts needed for the return but will be for audit (if needed). Sounds about right for a list but not sure about the 10%/year is it furnished?

The HMRC has a guide.

Phone calls to tenants
Travel costs for inspections
Postage for contracts
Gas safety certificate costs
Elec safety certificate costs

I think thats it, it all adds up.

You can claim all of the above as expenses. The 10% for depreciation only applies if it is let furnished.
I presume the GF has used all her personal tax allowance via her usual employment so just add up all the income and deduct all the allowable expenses. The balance will be taxed at her normal rate.
Check out rental tax

As well as the wear and tear allowance you can claim for repairs on fixture and fittings including integrated appliances. As Poolman stated claim travel costs, mileage at 45p per mile.